Steam generating apparatus and method



May 30, 1933. c. B. GRADY I STEAM GENERATING APPARATUS AND METHOD FiledSept. 28, 1923 4 Sheets-Sheet 1 May 30, 1933. c. B. GRADY STEAMGENERATING APPARATUS AND METHOD Filed Sept. 28 1923 4 Sheets-Sheet 2awoe/ntoz a GIT/1D! 4 Sheets-Sheet 3 CHARLES 5 All IIIII lllllll Y D Il-l A a All a |||||ll a AA N O o o o o a nu o o o o O o o a a I a o a o o0 a w 2 O U Q o O I $|l 7.

C. B. GRADY Filed Sept. 28 1925 STEAM GENERATING APPARATUS AND METHODMay 30, 1933.

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c B. GRADY STEAM GENERATING APPARATUS AND METHOD 4 Sheets-Sheet ,4

Fild Sept. 28 1923 Patented May 30, 1933 I PATENT OFFICE UNITED STATESCHARLES B. GRADY. OF WEST ORANGE, NEW JERSEY, ASSIGNOR TO METROPOLITANENGINEERING COIPANY, A CORPORATION 01' NEW YORK arm eanaaame a'rraaarusAND mrrnon Application am September as, was. Serial m. 885,266.

on line 3"--3 of Fig. 1;'

Fig is a longitudinal section on an enlarged scale of parts of the heatexchangers;

Fig. is a gartial end view of the same Figs. 6 and are an elevation andplan of a modified detail.

Referring to the embodiment of the invention illustrated, the powdered.coal or other fuel passes downwardly through nozzles 1 in a top wall 2into 'a chamber 3 which I call an oven. This is bounded by end walls 4and side walls 5, Fig. 3. The bottom of the oven 3 is open andcommunicates with a downwardly flaring chamber 6 which I call aprefurnace, havingflaring end walls 7 and parallel side walls 8, thelatter extending continuously to the bottom of the structure as shown inFig. 3. The end walls 7 of the pre-furnace are rounded outwardly attheir lower ends, where the chamber 6 communicates with a chamber 9which is of very much enlar ed size in the endwise direction, and whichcall a main furnace. This is bounded by the side walls 8, above referredto, and by end walls 10 at the outer ends of the structure. The walls 10connect at their bottom ends with downwardly tapering walls 11 forming asort of hopper which conducts the unburned solid particles to a trough12 from which they are removed by a current of water or any othersuitable ash conveyor.

The walls described are constructed of firebrick or other usual orsuitable material and may be supported by beams 13 and 14. The trough 12is preferably ofiset from the opening through which the ashesare-discharged into it, so as to minimize the absorption of heat fromthe furnace.

In the oven 3, the fuel will be dried and ignited so as to give it agood start toward combustion. 1

The two end walls 7 of the pre-furnace carry on their exposed facestubes 15 which communicate at their u per ends with crossboxesor.headers 16, which receive the feed water as hereinafter described.

By lining the pre-furnace 6 in this way, I provide extra evaporatingsurfaces exposed to the radiant heat of the burning mixture, and at thesame time I protect the walls from the action of the burning gases bycooling them. The tubes 15 communicate at their lower ends with boilers18, one at each end of the furnace 9 and which carry interposedsuperheaters 19.. The gases entering the main furnace 9 are divided intotwo streams which pass upwardly through the boilers and through a secondheat exchanger 22, being drawn therefrom by a fan 23 which dischargesthem through a horizontal duct 24 into a gas washer 25 comprising avertical duct 26 with an inclined wall down which a film of water ispassing and thence over a body of water accumulated in the bottom of thewasher.

The heat exchanger referred to is of a culiar design adapted'for usenot-only in t is connection, but in various other situations. Forexample, it may be used as anair cooler for cooling quantities of airthat are to be used to absorb the heat from the windings of electricgenerators and' similar apparatus.

Or it may be a plied to the cooling of automobile or aerop ane engines.In fact, its application as a cooler or as a heat exchanger maybewidelyvaried.

The heat exchangers are shown enlarged in Figs. 4 and 5. A plurality oftubes 27 in a parallel inclined positions are sealed at their ends andcarry a certain quantity of water or other suitable liquid 28 at theirlower-ends, these bein the ends over which the hot gases from the ilerfuel pass. Preferably air is exhausted from the tubes 27 to facilitateevaporation and condensation of the liquid them. The upper ends willgenerally carry vapor of the liquid contained in the tubes, and serve asa heater for the water or air, or

both, as hereinafter described. The tubes 27 may be connected to avacuum pump by which they could be kept free of air either continuallyor intermittently as circumstances re-' quire. e

The first heat exchanger comprises tubes- 27 which extend beyond theinner wall 29' of the flue for the combustion. gases. The smaller tubes36 of the secondheat exchanger 22 terminate at this wall. The differencein use-between these two exchangers isthat the lower or first one isused for heating both the feed water and the air which is supplied forcombustion; and the upper or second exchanger, since it takes gas at alower temperature, is used only for warming the feed water preparatoryto the additional transference of heat thereto in the first exchanger.This difference is illustrated in Figs. 1, 4 and 5.

"The long tubes 27 of the first exchanger abut against the outer wall 30of the gas flue and pass through the inner wall 29 thereof to asecondaryv supporting wall 31. The space between the walls 29 and 31 isenclosed to form a flue 32, Fig. 1, for the air supply. The air passesdown over the upper ends of the tubes and thence by suitable lateralpassages, as indicated by the arrows, to the nozzles 1 for mixture withthe fuel.

The ends of the long tubes 27 extend through the wall 31 and receivecertain 100 s of the feed water pipe. Such loops are in icated at33,Fig. 4. They'lie within the upper ends of the tubes 27 and areexposed to the heat of the vapor generated in said tubes by the hotgases from the boiler. The 100 s 33 attheir outer ends are connectedserial y by connecting tubes 34, the lowest loop in each seriesdischarging into a vertical pipe 35 which conveys it to the boiler ashereinafter described.

After the burnt gases have passed over the tubes 27 of the firstexchanger, there is very little heat remaining to be extracted from thegas. Consequently the second exchanger 22 is com osed of the shortertubes 36. These tubes, owever, are inclined and provided with more orless volatile liquid in their lower ends, the same as for the tubes 27of the first exchanger. Their upper sealed ends project through the wall29 of the'gas fine.

In order to secure the maximum extraction of heat from these tubes forthe feed water, the feed water pipe 37 Fig. 1) for each line enters theupper tube of a series at one end and has a portion 38 (Fig. 4) passingthrough-the upper zone in the tube 36' and shown alone.

I out at the other end to a connection 39 which leads to a length ofpipe 38 assing in the opposite direction through t e next lower tube andso on to the lowermost tube, from which theline passes by a length 40 ofpipe into the top tube 27 of the first exchanger;

I prefer to use about "twenty high of the lon tubes for' the firstexchanger and ten high of the short tubes for the second under ordinarysteam-generating conditions. The

number and the, sizes of the tubes, may, howmable; and though generallythese tubes will be exhausted of air above the liquid, this will notalways be necessary. Instead of using loops for the water in oneexchanger, and lengths of pipe passing from end to end through theother, I mayuse either one of these arrangements for both exchangers.Likewise, I may use for either or both exchangers a parallel flow ofwaterwith-the pipes connected to a common header or headers instead ofbeing connected by bends in the serial arrangement illustrated. Also Imay use either of the styles of exchanger In this connection it is to beobserved that the second exchanger which cools the gases and transfersthe heat there- 7 from to feed water alone is similar in pose to theordinary economizer.

In experiments which I made on a heat exchan er of this type with tubesof steel and with to es of glass, I have secured a much higher heattransfer in British thermal units per degree difference in temperatureper hour from the hot surface of the tubes to the air, and also from thevapor to the water in the pipes exposed thereto, than has been obtainedin the air heaters and economizers now generally in service. The datapurobtained indicate that the more nearly complete the air exhaustion,the better the heat transfer. They also indicate that the pressure inthe tubes will not rise to an amount that will distort them past theelastic limit, or burst them. With 20% of the space within the sealedtube filled with water and the remainder with water vapor and a smallamount of air and other foreign matters, the maximum pressure in thetube will not exceed about 500 the gasesstrikmg the lower tubes are atounds per square inch when about 900 degrees Fahrenheit, (which is abovethe usual maximum temperature).

The feed water pipes pass down through or alongside of the Walls to thecross-boxes or headers 16, previously referred to, communicatin with thetubes 15 and with the tubes 41 w ich are connected with the drums 42 ofthe boilers.

The complete steam generating unit described is particularly adapted tothe burning of pulverized fuel for the following reasons. The oven 3provides heat for driving off moisture from the coal and igniting it andgivin it an initial start toward complete com us'tion. The pre-furnace 6provides for progressive combustion, with in- 1 creasing volume, and atthe same time provides an increased heating surface of the boiler whichincreases its steaming capacity. In thls pre-furnacethe combustion iscontinuing and the exposed boiler surface is absorbing heat at areasonable rate, while also protecting the walls from excessive heating.The length of the oven and pre-furnace may be made such that thecombustion will be nearly complete at or near the top of the ofsecondary combustion or an excesslve amount of carbon monoxide in thegases passing through the boilerat high rates. The amount of airprimarily'admitted at or near the nozzles may be varied to suit thecharacteristics of the fuel used. A secondary supply of air may beadmitted at various points in the course of the fuel and gases.

For example, (as shown in the enlarged details, Figsl and 1") air may beadmitted from chambers 43 between the re-furnace walls 15 and the insideboiler walls 44 (these chambers being provided with openings 45) intosteel boxes 46, which support walls 4, and partially support cross-boxes16, and the air passing thence through suitable perforations into theupper end of the re-furnace 6. The air thus admitted serves a so to coolthe steel supporting boxes 46. It also serves to cool the blocks 47 and48 which surround the box 46 and thus to preserve them from excessiveheat and consequent destruction as well as the lower edges of the walls4 of the oven and the upper edges of the walls 15. of the pre-furnace.

Below the int described, it will not generall be advisable to providefurther air admission, for the reasons above stated. The large volume ofcross-section of the main furnace 9 provides space for a final completemixture of the products of combustion, and thus provides for completecombustion and the throwing out of the ash and slag.

The velocity of theproducts of combustion.

entering the main furnace may be relatively high because'of thecomparative restric tion in cross-section of the pro-furnace, and

this also will aid in the mixing together of the elements in the streamand will aid in the throwing down of the solid particles. Thetemperature at the lower portion of the main furnace will below comparedwith that in furnaces now generally in use, because of the absorption ofheat by the boiler surface exposed in the pre-furnace. The proportionallength of the latter, therefore, as well furnace, which will mean esstrouble from slag and less deterioration of the walls of the mainfurnace. I The upward turn of the gases before they pass over theprincipal water-carrying elements of the boiler, also aids in thethorough mixing of the gases. After these have turned upward they have astraight clean cut path through the single pass boiler, the superheaterand the heat exchangers; which means lowresistance and low, powerconsumption by the induced draft fan. This arrangement also permits themaintenance of high gas velocities without excessive drop in pressure,aswell as a com aratively great length of travel of the pro nets ofcombustion before they strike the principal elements of the boiler. Wethus insure almost perfect combustion. We are thus permitted to makethevelocity of the gases greater than in present practice, and to cut downthe furnace volume per ton of coal burned. Also the ash and slag thrownout will contain practically-no combustible matter, combustion beingcomplete when the gas streams turn upward.

One of the'principal objections to the use of powdered fuel isthe-nuisance from dust. In most plants now in operationover half of theas in the coal is carried out of the stack in the form of a fine dust.This is avoided in my steam generating unit by the interposition of aneflicient gas washer as- The tubes or containers of the heat ex-'advantage in view of the passing of the water pi through them.

he tubes exposedwithin the pre-furnace may be on the end walls only, asshown, or they may be also extended over the side walls.

Also they may be made larger, as at 15", Figs.

- larger tubes 6 and 7, so as to practically cover and entirely shieldthe wall 7 on which they are carried. The tubes 18! from the lower partof the boiler would then be expanded into or otherwise connectedto thelower ends of the The cross-box at the top may then be eliminated andthe circulating tubes 41 be connected directly to the tubes 7 Though Ihave described with great pa'rticularity of detail certainembodiments ofmy invention, yet it is not to be understood therefrom that theinvention is restricted to the particular embodiments disclosed. Variousmodifications thereof in detail and in the arrangement of the arts maybe made and the several features 0 improvement may be used in othercombinations by those skilled in the art without departure from theinvention as defined in'the following claims.

' What I claim is:

1. A single steam generating unit comprising a plurality of boilers, acommon furnace therefor having its greatest width below said boilers,and means'for directing gases of 1 combustion into said furnace andcausing to the place wherethey turjn.

them to turn at the zone of greatest width into separate streams throughsaid boilers, saidme'ans including water-cooled heat-absorbing surfacesalong which the gases flow 2. A single steam generating unit comprisinga pluralityof boilers, a common furnace therefor, and a pre-furnacehaving additional heating surfaces disposed along a pluhaving a widthsaid pre-furnace.

r'ality of walls thereof in whichthe ases of combustion are formed andvfrom which they pass to themain furnace, said main furnacesubstantially greater than '3. A single steam generating unit comprisinga plurality of boilers, acommon furnace therefor, and a pre-furnace inwhich gases of combustion are formed and from which'they pass to themain furnace and an oven in which the fueland air are mixed beforeentering said re-furnace, said main furnace having a widt "substantiallygreater than said prefurnace. Y

- '4. A single steam generating unit com a pair of oppositely arrangedboil- 'ers, a common furnace therefor having. its

greatest width'below said boilers and means fordirecting the gases ofcombustion down- 'wardinto said .furnace and causing them to turn upwardbelow said boilers into separate streams through said boilers, saidmeans including water-cooled heat-absorbing surfaces wall and exposedwithin said furnace, and a means for directin gases of combustiondownwardly throug saidfurnace and causing them to chan e direction andexpand and to pass upward t rough said principal water carryingelements.

6. A water tube boiler having radiant heat.

absorbing tubes and convection heat absorbing tubes, -a furnace inadvance of said convection heat absorbing tubes, a pre-furnace inadvance of said furnace, one wall of said re-furnace being lined withsaid radiant eat absorbing tubes and said re-furnace having anunrestricted outlet lea ing to said furnace and an oven in advance ofsaid prefurnace in which fuel and air areiadmitted and combined. a

7.- The method of producing's'teamwhich comprises creating an ignitedstream of fuel and air, exposing water to the radiant heat of.combustion, thereafter permittin 'gases of combustion to expand withoutsubthe hot stantial change in direction of flow, subdividing the streaminto lesser streams, changing I the direction of flow of said lesserstreams and passing said lesser streams separately in heat exchanrelationship with water after combustion in said streams hassubstantially ceased. I

8. The method of producing steam which comprises creating an ignitedstream of fuel and air, causing the stream to flow past hot radiatingsurface to assist in ignition and combustion thereof, passing the streamthereafter in heat exchange relationship with water while combustion inthe stream continues to a substantial'extent, permitting the stream toexpand without substantial change of direction and thereafter revert,and then tionship with water after combustion in said stream issubstantially complete.

9. A single steam generating unit comprising the combination of apluralityof separate boilers, a single main furnace therefor, a.pro-furnace disposed above the'main fur nace and having across-sectional area conpassing the stream in heat exchange rela- Illsiderably less than that of the main furnace,

certain of the defining wallsof said'pre-furs v nace being lined withwater-cooled heat-ab.-

sorbing elements, and means for leading ignited fuel and air through thepre-fui-nace in -a single stream into the main furnace and thence inseparate streams to said boilers.

10. In a steam generating unit, the combination of a plurality ofboilers, a single 7 ain furnace communicating with said boilrs, -apre-furnace disposed above the min furnace and having va cross-sectionalarea considerably less than that of the main furnace, certain of thedefining walls of said prefurnace being lined with water-cooledheatabsorbing elements, and means for leading ignited fuel and airdownwardly through the pre-furnace and into the main furnace and thenceupwardly in separate streams to said boilers.

11. In a steam generating unit, the combination of a plurality ofboilers, a single main furnace serving said boilers and disposed belowthem, a pre-furnace disposed above the main furnace and having acrosssectional area considerably less than that of the main furnace,certain of the defining walls of said pre-furnace being lined withwater-cooled heat-absorbing elements, and

means for leading an ignited stream of fuel and air downwardly throughthe pre-furnace into the main furnace, subdividing said stream intolesser streams and changing the direction of flow thereof in said mainfurnace and leading said lesser streams upwardly and independently tosingle boilers.

12. A furnace comprising an. entrance throat leading to a main chamberof substantially greater cross-sectional area than said entrance throat,water carrying tubes forming a part of the defining walls of said throatand extending into said main chamber and being spaced apart therein,said tubes extending across an outlet from said chamberthus forming awater cooled outlet, and said throat being provided with a refractoryentrance preceding said water carryv ing tubes, and means for directingfuel and air into said throat and discharging the products of combustionthrough said water cooled outlet.

13.. A furnace comprising an entrance throat leading to a main chamberof substantially greater cross-sectional area than said entrance throat,water carrying tubes forming a part of the defining walls of said throatand extending into said main chamber and being spaced apart therein saidtubes extending across an outlet from said chamber, thus forming watercooled outlets, and means for directing fuel and air into said throatand dischargin the products of combustion through said water cooledoutlets.

14. A- furnace comprising an entrance throat leading to a main chamberof substantially greater cross-sectional area than said entrance throat,water carrying tubes forming a part of the defining walls of said throatand extending into said main chamber and being spaced apart therein saidtubes extending across an outlet from said chamber, thus forming watercooled outlets, and said throat being provided with a refractoryentrance precedmg said water carrying tubes, and means for directingfuel and air into said throat and discharging the products of combustionthrough said water cooled outlets. 15. A furnace comprising an entrancethroat leading to a main chamber of substantially greatercross-sectional areathan said entrance throat, water carrying tubesforming a part of the defining Walls of said throat and extending intosaid main chamber and being spaced apart therein said tubes extendingacross an outlet from said chamber, thus forming a water cooled outlet,and said throat being rovided with a' refractor entrance preceding saidwater carrying tu s, one of the defining walls .of said refractoryentrance being provided with other water carrying tubes set behind theface of said wall, and means for directing fuel andair into said throatand discharging the products of combustion through sald water cooledoutlet...

16. In a steam generating unit the combination of a lurality of boilers,a common furnace there or disposed below said boilers, and a pre-furnaceabove said common furnace and having additional water-cooledheat-absorbing surfaces dis osed along a plurality of walls thereof, anmeans for introducing an ignited combustible'mixture into the prefurnacewhereby radiant heat of combustion ter carrying tubes exposed directlyto said gases, a boiler having a bank of tubes beyond said other walls,means for supplying fuel for ignition and preliminary combustion in saidpassage, andmeans for leading the gases of combustion along said otherwalls and through said bank of tubes.

18. A steam enerating unit comprising a refractory-linen? passage, meansfor introducing a combustible mixture into said assage for ignition andpreliminary com ustion therein, diverging defining walls beyond 1 saidpassage for directing the flow of gases issuing from said passage andpermitting the gradual expansion of said gases, water-carrying elementson said defining walls exposed directly to said gases, a chamber beyondsaid defining walls to which the gases are led, an outlet from saidchamber, a bank of tubes beyond the outlet, and means for drawing gasesof combustion from said passage along said" defining walls and throughsaid chamber and said bank of tubes. 7

19. A steam generating unit comprising the combination of a lurality ofboilers having their tube banks'm end-to-end alignment, a

common furnace therefor having its greatest dimension parallel to theaxes of the said tube banks, a pre-furnace having water-cooled ,wallsdisposed above said furnace in com 5 munication therewith, and means fordirecting the gases of combustion through said prefurnace downwardlyinto said furnace, causing them to turn upward at the zone of greatestdimension to flow in separate streams throu h said boilers.

- 20. n a furnace for burning powdered fuel, the combination of a boilerhaving heating surfaces so arranged as to provide a lcw- -er combustioncompartment, walls extendin 15 above the boiler and arranged inwardly othe boiler heating surfaces to provide. an upper combustion compartmentin vertical alignment with the 1 lower compartment, the upper and lowercompartments forming a vertically disposed combustion chamber, andmeansfor feeding powdered fuel and air into the upper compartment. I Inwitness whereof, I have hereunto signed my name. 26 CHARLES B. GRADY.

